Ellipsometry as a probe of crystallization kinetics in thin diblock copolymer films

Abstract

ABSTRACT:We present results on the use of ellipsometry as a novel probe for the crystallization kinetics in thin films of a diblock copolymer. Ellipsometry makes use of the change in polarization induced upon the reflection of light from a film-covered substrate to enable the calculation of the refractive index and thickness of the film. The information obtained with these measurements can be compared with information from differential scanning calorimetry, with the additional advantages that small sample volumes and slow cooling rates can be employed and that expansion coefficients can be determined. By studying the temperature dependence of these quantities, we are able to measure the crystallization kinetics within very small volumes ($10 À10 L) of a poly(butadiene-b-ethylene oxide) diblock copolymer. Through a comparison of two different poly (ethylene oxide) block lengths, we demonstrate a reduction in both the crystallization and melting temperatures as the domain volume is reduced.

Are polymers glassier upon confinement?

“…Temperature-dependent ellipsometry measurements, [13][14][15] allowed detecting phase transitions in PLLA films as thin as 6 nm. Focusing on the thickest samples, the transitions in the ellipsometric angles occur in proximity of the values of the glass transition (T g ), cold crystallization (T CC ) and melting temperature (T m ) found by differential scanning calorimetry operated in comparable experimental conditions.…”

Confinement Effects in Polymer Crystal Nucleation from the Bulk to Few-Chain Systems

“…Over the entire range in droplet volumes, both molecular weights were found to crystallize at the same T c , within the scatter of the data. For comparison, crystallization measurements were also made on diblock copolymer films, where PEO is the minority component and forms spheres within a polybutadiene (PB) matrix [21]. Two block lengths were studied (PEO-PB molecular weights: 4.5-26 and 6:8-26 kg=mol), and the results are shown as triangles in Fig.…”

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“…In previous work, we have demonstrated the ability to study crystallization within minority domains of thin sphere‐forming diblock films using ellipsometry 37. Ellipsometry is a technique that is complementary to more standard tools like DSC and affords a few advantages.…”

“…While previous measurements of nano‐confined crystallization in diblocks has typically been carried out with DSC,14, 15, 17, 19, 21 here we use ellipsometry to probe crystallization 10, 36–38. Ellipsometry exploits the fact that linearly polarized light emerges elliptically polarized when reflected from a film covered substrate to obtain the thickness and index of refraction of a film 36.…”